Global warming's effects may hit tropics hard, a study says

WASHINGTON — Although the most significant harm from climate change so far has been in the polar regions, tropical plants and animals may face an even greater threat, say scientists who studied conditions in Costa Rica.

"Many lowland tropical species could be in trouble," the team of researchers, led by Robert K. Colwell of the University of Connecticut, warn in today's edition of Science.

"The tropics, in the popular view, are already hot, so how could global warming harm tropical species? We hope to put this concern on the conservation agenda," Colwell said.

That's because some tropical species, insects for example, already are living near their maximum temperatures and warmer conditions could cause their numbers to decline, Colwell explained.

The researchers estimated that an increase of 5.8 degrees over a century would make 53% of the 1,902 lowland tropical species they studied subject to attrition.

But that doesn't mean jungles will one day be barren.

"Some species will thrive," Colwell said. "But they are likely to be those already adapted to stressful conditions," such as weeds.

There are few cooler locations nearby for tropical plants and animals to escape rising temperatures.

In the tropics in particular, going up rather than out may be an answer.

That's because tropical species with small ranges would have to shift hundreds of miles north or south to maintain their current conditions. "Instead," Colwell said, "the most likely escape route in the tropics is to follow temperature zone shifts upward in elevation on tropical mountainsides."

For example, the researchers said, temperature declines 9.4 degrees to 11.7 degrees for every 3,280 feet of altitude gain. To get a similar reduction by moving north or south, you would have to travel more than 620 miles.

Of course, moving won't always work; species already living on mountaintops will have no to room to climb.

Meanwhile, a separate paper in Science reported that warming climate has already scrambled the ranges of small mammals in Yosemite National Park.

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